diff --git a/spring-core/src/main/java/org/springframework/core/Constants.java b/spring-core/src/main/java/org/springframework/core/Constants.java
index c18b8d289528..048dd0bc941d 100644
--- a/spring-core/src/main/java/org/springframework/core/Constants.java
+++ b/spring-core/src/main/java/org/springframework/core/Constants.java
@@ -264,7 +264,7 @@ public Set<Object> getValuesForSuffix(String nameSuffix) {
 	 * @throws ConstantException if the value wasn't found
 	 */
 	public String toCode(Object value, String namePrefix) throws ConstantException {
-		String prefixToUse = (namePrefix != null ? namePrefix.trim().toUpperCase(Locale.ENGLISH) : null);
+		String prefixToUse = (namePrefix != null ? namePrefix.trim().toUpperCase(Locale.ENGLISH) : "");
 		for (Map.Entry<String, Object> entry : this.fieldCache.entrySet()) {
 			if (entry.getKey().startsWith(prefixToUse) && entry.getValue().equals(value)) {
 				return entry.getKey();
diff --git a/spring-core/src/test/java/org/springframework/core/ConstantsTests.java b/spring-core/src/test/java/org/springframework/core/ConstantsTests.java
index ee7b7187eb12..47342b35b511 100644
--- a/spring-core/src/test/java/org/springframework/core/ConstantsTests.java
+++ b/spring-core/src/test/java/org/springframework/core/ConstantsTests.java
@@ -148,19 +148,28 @@ public void testToCode() {
 		assertEquals(c.toCode(new Integer(0), "D"), "DOG");
 		assertEquals(c.toCode(new Integer(0), "DO"), "DOG");
 		assertEquals(c.toCode(new Integer(0), "DoG"), "DOG");
+		assertEquals(c.toCode(new Integer(0), null), "DOG");
 		assertEquals(c.toCode(new Integer(66), ""), "CAT");
 		assertEquals(c.toCode(new Integer(66), "C"), "CAT");
 		assertEquals(c.toCode(new Integer(66), "ca"), "CAT");
 		assertEquals(c.toCode(new Integer(66), "cAt"), "CAT");
+		assertEquals(c.toCode(new Integer(66), null), "CAT");
 		assertEquals(c.toCode("", ""), "S1");
 		assertEquals(c.toCode("", "s"), "S1");
 		assertEquals(c.toCode("", "s1"), "S1");
+		assertEquals(c.toCode("", null), "S1");
 		try {
 			c.toCode("bogus", "bogus");
 			fail("Should have thrown ConstantException");
 		}
 		catch (ConstantException expected) {
 		}
+		try {
+			c.toCode("bogus", null);
+			fail("Should have thrown ConstantException");
+		}
+		catch (ConstantException expected) {
+		}
 
 		assertEquals(c.toCodeForProperty(new Integer(1), "myProperty"), "MY_PROPERTY_NO");
 		assertEquals(c.toCodeForProperty(new Integer(2), "myProperty"), "MY_PROPERTY_YES");